A mobile communication system is equipped with a function of calculating a location (or coordinate) of a user equipment to provide a LCS (location service) providing the location of the user equipment. Currently, there are various methods of calculating the location of the user equipment including a cell ID (identifier) method delivering an identifier of a cell to which the user equipment belongs thereto, a method of calculating the location of the user equipment via triangulation measuring time taken by a radio signal transmitted from the user equipment to arrive at each base station, a method of using a satellite and the like.
First of all, according to the cell ID-based (e.g., cell coverage) method, a location (or coordinate) of a user equipment can be measured by identifying a serving base station to which the user equipment belongs thereto. Information on the serving base station and a cell can be obtained in a manner of performing a paging procedure, a locating area update procedure, a cell update procedure, a URA (UTRA/UTRAN registration area) update procedure or a routing area update procedure.
Cell coverage based positioning information can be indicated by a geographical coordinate related to a serving cell or a cell identifier of a cell used as a service area identifier. The positioning information may include QoS (quality of service) estimation (e.g., related to obtained accuracy). If available, the positioning information may include a positioning method (or a list of the method) used for estimating a location.
When a geographical coordinate is used as location information, an estimated location of a user equipment may correspond to a fixed geographical coordinate in a serving cell (e.g., a coordinate of a serving base station), a geographical center of a serving cell coverage area or a different fixed coordinate in the cell coverage area. And, the geographical coordinate can be obtained by a combination of a cell-specific fixed geographical coordinate and different available information (e.g., RTT (round trip time) in a FDD system, recognition of user equipment timing advance in a TDD system, reception timing deviation measurement or the like).
According to the method of using a satellite, a user equipment should be equipped with a radio receiver capable of receiving a GNSS (global navigation satellite system) signal. As an example, the GNSS can include a GPS (global positioning system), Galileo system and the like. In order to determine a location of a user equipment, GNSSs (e.g., GPS, Galileo and the like) different from each other can be used in a manner of being individually or being combined with each other.
The method of using the triangulation technology can be classified into two types. One is a U-TDOA (uplink-time difference of arrival) positioning method and another one is a OTDOA-IPDL (observed time difference of arrival with network adjustable idle periods in downlink) method.
First of all, the U-TDOA positioning method is performed based on a measurement of a network measuring TOA (time of arrival) of a predetermined signal (e.g., a pilot signal, a reference signal), which is transmitted by a user equipment and received by a plurality of LMUs (location measurement units). In order to precisely measure a TOA of a burst (i.e., a predetermined signal) using the U-TDOA positioning method, it is required that a plurality of the LMUs to be geographically positioned in the vicinity of the user equipment. Since geographical coordinates of a plurality of the LMUs are known, a coordinate of the user equipment can be calculated using a hyperbolic trilateration scheme. In most cases, it is not necessary for a user equipment deeply positioned at a cell coverage radius to receive a signal from a different cell. It is necessary for the user equipment to listen to a signal from the different cell only when the user equipment moves to a cell coverage boundary and the user equipment can make a handover to the different cell. The aforementioned operation can be arranged to the U-TDOA positioning method, which needs to listen to at least one cell irrespective of a geographical location of a user equipment. Secondly, the OTDOA-IPDL method indicates a method of measuring a location of a user equipment using timing differences of which signals transmitted by each cell are arrived at the user equipment.